Study On The Soil Chemical Consolidation And Tomb Slope Stability Of Xiongjiazhong Site

Earthen sites are the places where human live, produce, and make cultural and religious activities. The sites carry the civilization history of the Chinese nation, and reflect human production activities, social activities, social relations, economic and cultural development level in a certain historical period, so they are our object to study of ancient culture information today. Earthen sites are carefully selected for location and special processing at the time, due to influencing by natural and environmental factors for a long time, all kinds of environmental geological diseases happened, human engineering activities aggravate the damage of the sites, or even endangered.Earthen sites lie in certain geological environment, all kinds of diseases were controlled by many influence factors including the engineering geology, hydro-geology and environment, earthen sites protection should combine these factors. At present many scientific research institute in northwest arid region have made many successful experiences about earthen sites protection, because of humid and rainy climate conditions, environmental geological diseases in southern is different from that in northern, the corresponding diseases mechanism and control measures are also different, less research are focused on this area.Xiongjiazhong site is located in Jingzhou City, Hubei Province which is characterized with humid rainy weather, the site consists of main burial, accompanying burial, chariot pits, sacrificial tomb, burial pits, etc., it covers an area of 110,000 square meters, it is the largest and best preserved, most complete mausoleum distribution, and first-class noble Chu churchyard, the in-situ protection is of great significance.After several grave damage and the influence of the production and construction, Xiongjiazhong site preservation environment suffered severe damage, the National Heritage Board formally approved the rescued archaeological excavations for chariot pits and parts of human’s tomb in November 2005. In the process of excavation, it was discovered that the main environmental geologic diseases for Xiongjiazhong site include water-caused trouble, grave slope surface peeling off and falling phenomenon.In this paper, engineering geological and hydro-geological conditions for Xiongjiazhong site were investigated by means of engineering geological field work, laboratory experimental research for evaluation of engineering properties of soil. In the basis of aforementioned analysis, the factors leading to environmental geologic diseases were summarized as expansive soil in sites, humid and rainy climate conditions, and the human engineering activities. This paper gave emphasis on factors affecting the strength of expansive soil, seepage and slope stability in the study area were estimated through numerical simulation, the physical and mechanical properties of the soil after chemistry strengthening, combining experimental and numerical results, site protection measures for earthen sites was proposed. The details of research contents and achievements are as follows:1. Investigation of geographical location, natural environment, topography, lithology, geological structure, hydro-geological conditions and the main environmental geological diseases in earthen sites.2. Research of soil material composition, structural characteristics, physical properties, shear resistance, compressibility, permeability, swelling shrinkage, and discriminant classification of expansive soils based on comprehensive test results, the results show that the first layer is the weak expansive soil, the second and third layer belong to the moderate expansive soils. What’s more, the swell-shrink property of soil increased with the increasing of buried depth.3. The cracks were generated and developed since expand with wet and contact with dry under atmosphere for expansive soil which is key component in the tomb pit slope. On the one hand, the presence of cracks weaken the slope soil structure, on the other hand, the cracks provide water seepage channel that make the soil strength reduced, and threaten the stability of the slope. In this paper, the influence factors on expansive soil shear strength were studied through laboratory testing.Direct shear test were carried out to study expansive soil strength changing with the moisture content, the experimental results showed that the remoulded sample shear strength parameters decreased exponentially with the increasing of moisture content, in addition, the influence of moisture content on the cohesion is greater than the effect on internal friction angle.Direct shear test were carried out to study the changing rule of the strength of expansive soil under dry-wet circulation condition, the results showed that shear strength parameters of the remoulded sample decreased with the increasing of dry-wet cycles, there was a significantly reduce for strength parameter of soil after first dry-wet circulation, and trended to be stable after experiencing four times dry-wet circulations. Additionally, the impact of dry-wet circulation on cohesion is larger than that on friction angle, and dry-wet circulation has more influence on the soil with higher swelling shrinkage.The soil water characteristics’of expansive soil in ancient sites area was analyzed using pressure plate apparatus. The Van Genuchten model parameters were obtained according to fitting the test results in Matlab software. Comparing VG model parameters of different layer soil, it was found that inlet value and residual water content increased gradually as the buried depth increasing, while the slope of soil water characteristic curve gradually decreases, and it suggests that the water-holding capacity of soil in ancient sites area is gradually enhanced. Test results of the Chapter 3 is that clay content, plasticity index, expansion potential, day density, saturation moisture content gradually increase with increasing of buried depth. Regarding to soil water characteristic test results, there were a good agreement between pressure plate apparatus and VG model research and laboratory tests.Unsaturated soil direct shear apparatus were conducted to study the unsaturated shear strength of expansive soil, setting the axial pressure of 100 kPa, the unsaturated strength was evaluated under different matrix suction. It can be illustrated in results that the shear strength increases with the increase of matrix suction, and corresponding displacement at the peak shear strength also increases with the increase of matrix suction. That is to say, when the matrix suction increases, the ability to resist damage of soil will increase so that the corresponding plastic deformation is also increased. Taking non unsaturated direct shear test results into Fredlund shear strength formula, assuming that the friction angle φ’ is not affected by the matrix suction, in this case, the calculation results shows that the friction angle φb decreases with the increase of matrix suction. For example, the matrix suction increases from 50 kPa to 150 kPa, friction angle φb rapidly decreases, and the matrix suction is greater than 200 kPa, the friction angle φb slowly decreased.4. Numerical model is built to calculate the underground water seepage field in the relics and the slope stability of the main tomb pit, adopted the test results of the water permeability parameter and strength parameter given in the chapter 3 and chapter 4.The water seepage field in rain of the main tomb pit slope shows the influence of rain increase the surface soil water content and decrease the metric suction. As the rain lasting, the surface soil tends to the saturation, forming the transient saturation section and an expending region downwards. In the rain, the slope toe is the first to get saturated, and the saturating time reduces as the rainfall intensity increases.Based on the seepage field, the water supplementary amount of the slope is calculated, considering the Scenery Lake, rainfall and confined groundwater. The result shows that in the supplementary amount down order, they are the rainfall, the confined groundwater and the Scenery Lake. Therefore eliminating the rainfall infiltrating supplement should of the highest priority. The paper presents to removing the rainfall influence by impervious blanket and drainage ditch. Since the confined groundwater has little amounts of water supplement, the blind drainage ditch is distributed to dredge the underground water in a certain region, freeing the bottom of main tomb pit from groundwater impact.The stability calculation of the main tomb pit slope:(1) The slope stability calculation considering rainfall reflects the drop of slope stability coefficient as the rainfall intensity and duration rise, so with the lowering range of slope stability coefficient. (2) The calculation with the climatic zoning method shows that the slope stability is low with the stability coefficient of 0.939. The risky slip surface buries in a shallow region, and the damage starts from the slope toe.5. For the strength dropping in swelling soil slope under the influence of atmosphere, the chemical grouting method is recommended to relieve the threat of slope failure, meanwhile leaving the relics intact. The chemical grouting method is to distribute consolidation chemicals on the soil surface, preventing the rain from infiltrating and the soil from cracking, thus to eliminate atmosphere impacts and to enhance the hydraulic stability and strength, reaching the goal of stabilizing the slope.The consolidating material in the relics is the soil stabilizer selected through on-site experimental methods. The comparative laboratory test indicates that the consolidated soil is of nearly no swell-shrink characteristic and fine hydraulic stability, also showing a certain increase in strength.To study the influence to the infiltrating depth of soil stabilizer made by the soil initial moisture content, the experiment is conducted on the remolded soil samples of three different moisture contents, based on minimum natural moisture contents, moisture contents to the air-entry value and plastic limits. In the test, soaking reinforcement is adopted to inspect the infiltrating depth, the infiltrating amount and the strength. The test results reveal that the infiltrating depth and the infiltrating amount reach the maximum under the water content of 17.50%.The structural variation in the soil consolidating and before is compared through the scanning electron microscope (SEM) method, which shows the soil alteration from the loose flocculent structure to the relatively compact static flow structure. In this way, the soil particles contact with each other from the surface-to-edge form to the surface-to-surface form, making the consolidated soil of better hydraulic stability and better mechanical strength.6. The managing measures of geological diseases were put forworded in Xiongjiazhong site.1) Drainage and waterproof engineering eliminate water-caused trouble.2) Spraying chemical reinforcement agent and buring soil nail reinforce the main tomb pit slope.Concluding the on-site investigation, laboratory test and numerical calculation, the reason for the Xiongjiazhong site environmental and geological disease is revealed. The main internal cause is the expensive soil of the site. The external cause is that the rainy climate condition and human construction damage the previous isolated environment, leading to the explosion of expensive soil, and finally causes the diseases. The paper lastly combines the disease character and mechanism and put forward the practical managing measure, under the principle of relic protection, offering the region an appropriate geological environment. Through the research on the Xiongjiazhong sites protection, the achievement may be used for reference in the earthen sites protection in the southern moisture areas.